This invention relates to apparatus for and methods in brachytherapy. More particularly, this invention relates to apparatus for and methods of accurately depositing radioactive seeds in a patient's body in a brachytherapy by calculating radiation dose distribution.
In the field of medicine, nuclear radiation may be used for diagnostic and therapeutic treatment of patients inflicted with cancer. Typically, more than half of these patients need radiation therapy either as a primary or as an adjunct mode of treatment. Conventional medical radiation sources used in these treatments include large fixed position machines such as linear accelerators as well as small, transportable radiation generating probes which provide a boost therapy. In the latter treatment system, a miniaturized probe capable of producing a high dose of radiation in a pre-defined geometry is inserted into a treatment volume. The treatment is commonly referred to as brachytherapy because the radiation source is located close to or, in some cases, within the treatment volume. Brachytherapy is advantageous in that high doses of ionizing radiation, measured in terms of energy/mass, are delivered to a localized volume of tissue such that the radiation is supplied primarily to the treatment volume without significantly affecting tissues in adjacent volumes. This ability, when combined with a rapid reduction in the radiation dose as a function of distance, shields distant anatomies from spurious radiation. Hence, the technique has provided excellent results for localized control of various tumors.
In applications where tumors under treatment are in the patient's prostate gland, an applicator such as a perineal template is commonly employed with one or more probes that contain seeds or radiation sources. The template has an array of openings for accepting a plurality of sequential tandem brachytherapy probes or needles. During operation, the template is positioned near tumors to be treated and referenced to one or more scanned images before the seeds are inserted into the openings.
During a brachytherapy operation, a physician needs to know exact positions of the seeds, as well as a radiation dosage distribution from these seeds. Additionally, it is desirable to quantify the radiation received by surrounding organs. Generally, locations and orientations of the needles are referenced to one or more images derived from modalities such as X-ray radiograph, computed tomography (CT), magnetic resonance (MR), ultrasound, or nuclear medicine scans of the patient.
Typically, for prostate cancer, images from a base to an apex of the prostate are obtained at 0.5 centimeter increments. Information on adjacent rectum, urethra and bladder is also captured. The information is correlated with the position of the applicator, which in turn is used as a reference for determining the needle position. The position of the seed inside the patient is determined relative to the needle and the template as a function of the needle length and orientation, minus a length of a remaining needle portion outside of the template.
The seed position determination process discussed above is laborious and is subject to operator errors and inaccuracies associated with the needle insertion. One source of error is the bending of the needle when it encounters a rigid anatomical portion. Another kind of error may be in the transformation of scanned image data to a coordinate system fixed to the patient's body. Yet another kind of error may be in the equipment calibration or usage.
In addition to the seed position data, information on the radiation dose distribution is also needed. If the radiation dose distribution at a target point is too low due to unforeseen conditions, the brachytherapy operation may be ineffective. If the radiation dose distribution at the target point is too high, the operation may have undesirable effects. Traditionally, the dose distribution analysis involves entering into a dosimetry computer the contours of the prostate, the urethra and the rectum target volume. Seed positions and seed strengths are then entered into the dosimetry computer. Based on the data entry, the dosimetry computer determines a dose distribution estimate. The data entry process is tedious and error-prone. Moreover, without a visual feedback, such dose distribution analysis is prone to accumulated errors. As noted above, furthermore, potential errors associated with the needle insertion process may affect the reliability of the seed position determining process.